Work Function-Tunable Graphene/Wo3 Heterojunctions for High-Performance Photoelectrochemical Cell: Uv-Treatment Effect and Defective Graphene

Abstract

Designing hybrid photoelectrodes with graphene capable of efficient charge-carrier transfer and excellent chemical stability is an effective strategy for developing high-performance photoelectrochemical (PEC) cells. However, it remains unclear how the PEC properties are enhanced and how to control the junction properties in graphene/metal oxide heterojunction-based photoelectrodes. Here, we develop the deterministic junction to enhance PEC performance in graphene/tungsten trioxide (WO3)-based photoelectrodes by tuning the work function of graphene. It reveals that the band structure of graphene/WO3 heterojunctions can be modified by ultraviolet (UV) treatment on WO3 thin films. This modification is supported by the observation that single-layer graphene/UV-treated WO3 photoelectrode exhibits significantly enhanced PEC activities toward oxygen evolution reaction (OER) (evidenced by features like a threefold increase in photocurrent, an onset potential shift, and improved stability), whereas the single-layer graphene/untreated WO3 electrode demonstrates improved properties for hydrogen evolution reaction (HER). Additionally, defects in the graphene layer formed during PEC water splitting contribute to high catalytic activities of the graphene/WO3 photoelectrode due to a decrease of Gibbs free energy for OER and HER. These results emphasize that the band structure engineering via work function tuning in graphene/WO3 heterostructure can provide multiple benefits for a high PEC performance and long-term stability.

Keywords: photoelectrochemical water-splitting, tungsten trioxide, graphene, work function, Heterojunction